The present invention relates generally to semiconductor chip architecture. More particularly, it relates to a position-sensing system for a microelectromechanical systems (MEMS) device.
In the field of microelectromechanical systems (MEMS) devices, portions of a semiconductor wafer, such as a memory in a computer system, may move relative to other parts of the wafer. For example, a memory portion of a computer chip may store data written to it and read from it by read/write heads. A MEMS device may use stationary read/write heads that access a moveable memory portion. The memory portion may move relative to the read/write heads using an actuator motor. The moveable structure is referred to herein as a xe2x80x9cmover.xe2x80x9d
In one use, a MEMS device may use a mover that moves in two dimensions, X and Y. For example, the mover may be part of a mover layer of a three-layer wafer system. The mover is connected to other portions of the mover layer by spring devices, or flexures. Flexures allow the mover to move in two dimensions, while suspending the mover between the layers, and while urging the mover back to a static position, or mechanical equilibrium. Flexures may include coupling blocks to control movement of the mover. A motor causes the mover to move within the layers.
MEMS devices allowing a mover to move in two dimensions are known. In order to effectively use the MEMS device, it is desirable to know the position of the mover, in terms of its X and Y coordinates. In the memory example with read/write heads, the MEMS device would have to know where the mover is in order to know which portion of memory is being accessed. Existing systems use capacitor plates located on the mover to determine its position. For example, one plate may be located on the mover and the other plate may be located on a stationary portion off of the mover. The overlap of the plates creates a capacitor that changes in capacitance depending upon the position of the mover, based on the equation       C    ∝                            ϵ          o                ·        A            d        ,
where C is the capacitance, xcex5o is the dielectric constant, A is the area of overlap between the capacitive plates, and d is the distance between the plates. Various ways are possible to create capacitances that depend upon the position of the mover. The area of overlap or the distance between the plates can be changed by moving the mover, thereby changing the capacitance between opposing plates. The problem with existing methods is that they position the capacitive plates on the mover, thereby consuming a portion of the mover that would otherwise be available for productive use, for example, as memory. What is needed is a way to determine the position of the mover without consuming valuable space on the mover.
A microelectromechanical system (MEMS) device is disclosed for determining the position of a mover. The MEMS device has a bottom layer connected to a mover layer. The mover layer is connected to a mover by flexures. The mover moves relative to the mover layer and the bottom layer. The flexures urge the mover back to an initial position of mechanical equilibrium. The flexures include coupling blocks to control movement of the mover. The mover moves primarily in two dimensions, staying substantially in the same plane as the mover layer, such that the distance from the mover to the bottom layer stays substantially constant as the mover moves. The MEMS device determines the location of the mover by determining the capacitance between mover electrodes located on the coupling blocks of the flexures and counter electrodes located on an adjacent layer. The coupling block moves according to a determinable relationship with the mover. For example, movement of the coupling block may be directly proportional to movement of the mover. As the coupling block moves, the capacitance between the mover electrode and the counter electrode changes. A capacitance detector analyzes the capacitance detected between the electrodes determines the position of the mover. In one embodiment, the mover may be used as a memory to store information written by and read from read/write heads positioned on the top or bottom layers. The mover moves using an actuator motor to enable data to be written to or read from the desired location on the mover. In one embodiment, the mover layer and the bottom layer are part of a single semiconductor wafer.
A MEMS device is also disclosed for a three-wafer semiconductor device having a mover layer connected to a top layer and a bottom layer, in which each of the layers is a separate wafer. The mover layer is connected by a flexure to a mover. The flexure includes a coupling block for controlling movement of the mover. The coupling block has a mover electrode, and the top or bottom layers, or both, have a counter electrode. A capacitor is created between the mover electrode and the counter electrode, which capacitance changes as the mover moves. A capacitance detector determines the position of the mover based on the capacitance.
A flexure is also disclosed for connecting a mover to a layer. The flexure allows the mover to move relative to adjacent layers and uses a coupling block to control movement. Movement of the coupling block is known relative to movement of the mover. The coupling block of the mover has a mover electrode for determining the position of the mover based on a capacitance detected on the mover electrode. The capacitance detected by the mover may be used in conjunction with capacitances detected on other mover electrodes on other coupling blocks of other flexures to determine the mover""s position.